Controlling Modbus write multiple length

[timun]

In the Modicon Modbus controller settings, the 'max block size (words)' controller parameter defines the maximum number of registers than can be read in a single 'read holding registers (0x03)' command. The actual number of registers read in a single command depends on the tag array size or string length, subject to the max block size defined.

Is there an equivalent way to set the number of registers that are written in a 'write multiple holding registers (0x10)' command? It appears that the controller always divides a write into sets of 8 words, and this is causing me problems due to the quirks of a particular Modbus slave that expects an entire string to be written in a single command.

[Chris T.]

Hi timun,

This should not be too difficult, you will first want to set the "Holding/Input registers per message (write)" to your desired string length. Enable the "Force function code 0x10" parameter. And then just write to your string. It should copy your string as far as it is populated.